Setting is 20 minutes into future - everything is as we know it, or as we can reasonably predict, except the zero-tau capsules.

Capsule is a thin mesh of Unobtanium connected to a portable Handwavium reactor. When turned on, time inside does not flow. Details "by the numbers":

  1. It is unclear if time inside actually stopped or is just extremely slowed down. A [insert reasonable time here]-long experiment did not show any measurable time inside (in other words, you may adjust this).
  2. Starting field up and shutting it down can be instantaneous, or take as long as 10 seconds during which time inside slows down or speeds up.
  3. Field border is sharp, around 1ℓP. We put it in the middle of metal plates that are casing for capsule, to prevent anything from interacting directly with such border (or in near-vacuum between plates, if interactions with metal would be a problem - again this is adjustable).
  4. Unobtanium mesh is supposed to be something that creates the field, but has no other uses or effects - it does not shield anything from anything, does not get old, nothing. Thus, it shouldn't matter if it's in or out. Probably out, because getting it destroyed would be a good story element, but that's something for another question. Similarly with Handwavium reactor. Please ignore them where possible, their only meaningful effect should be existence of the zero-tau field.

That way, trip to Mars can be as short as 30 seconds, from the passenger point of view.

The problem is: How to safely exit?

Metal walls of the capsule can stop anything bigger than hydrogen atoms, and slow down other things. But that is still around seven months of cosmic radiation, atoms leaking in thorough the seal etc, released in a very, very short time. Sudden gravity change would not help, and probably there are things that I haven't thought of, too.

So, how would we make it safe for our travelers? I want them to survive and I do not want any neural or perception damages. Other than that I can live with, as long as it heals, at least in early stages when we are only setting up Mars operations. We need to get passengers healthy when we go to commercial flights, but if it is too difficult, it can wait.

  • $\begingroup$ This was in sandbox: worldbuilding.meta.stackexchange.com/a/6790/809 (10k link now). Posting because I think that it is good enough, even if not great. Got very little attention in Sandbox, so I am still open to improvements. $\endgroup$
    – Mołot
    Oct 22, 2018 at 20:23
  • 2
    $\begingroup$ You should add a warning to that TVTropes link. I got stuck there for an hour. $\endgroup$
    – Mermaker
    Oct 23, 2018 at 19:22

3 Answers 3


Your zero-tau capsules are the ideal solution for their own problem:

You state that all radiation and particles that hit an active capsule are slowed down and released in a burst when the capsule is shut off. That means not only is the inside shielded while the capsule is active, but anything behind the capsule as well. These capsules are now a perfect shield that can stop even neutrinos or gamma radiation.

So, surround each passenger-capsule on all sides with other capsules, that are empty or contain cargo; then no radiation can hit the capsules in the middle. Just make sure to take the outer capsules far away before switching them of.

Or better yet: surround your whole spaceship with shield capsules. Perhaps multiple layers, in case anything goes wrong.

  • 2
    $\begingroup$ Sneaky! Thin sheet of zero-tau would indeed do the trick. Good job! $\endgroup$
    – Mołot
    Oct 23, 2018 at 9:39
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    $\begingroup$ If you double-layer and connect the Unobtanium as a very thin toroid/cylinder (think of 2 cups inside each other), that would still act as shielding, while being about the same shape as a standard spacecraft/shipping container. Your 0τ capsules are stored inside, and removed at the destination. Every so often, the Spaceship is taken somewhere safe and the field is turned off/on to clear-down - much like degaussing $\endgroup$ Oct 23, 2018 at 10:19
  • $\begingroup$ capsules that have been used as shields that have been hit with a lot of radiation or particles (in a space-warfare like scenario) could also be used as weapons. simply jettison or launch the capsules towards an enemy ship not equipped with such capsules and remotely switch them off $\endgroup$ Jan 31, 2022 at 2:38

Who says you have to have the field in unbroken operation for the whole trip?

Sensors near the "event horizon" monitor the exposure of the capsule to external radiation. When a pre-set safety threshold is approached, the capsule switches off for a small amount of time (whatever the minimum cycle time for the field - power off and back on - is, plus a small delay to allow the passenger to properly absorb/emit/adjust to the radiation), allowing the particles to strike the occupant while they are still at a safe level, and allowing gravity (and other fields) to adjust in smaller increments.

This might increase the length of the trip from the occupant's perspective, but as the shielding gets better, these interruptions can be reduced, perhaps to the point that you only need five or ten per trip, each lasting 20 seconds or so (10 second spin-down and 10 second spin-up in your extreme case). Even with modern day shielding the number of cycles would probably only be on the order of 5 or so a day, making a 300 day trip take 100 minutes from the passenger's point of view. Rounding, we can call it two hours, and the best thing to do would be to render the passenger unconscious for the journey anyway, so that two hours would be a pleasant nap.

If the cycle time was near instant (the lower bound of your power on/off range), then a conscious passenger simply gets a time lapse view of the trip lasting a few dozen seconds, which could be seen as a feature.

In either case, some form of anti-radiation treatment and a shielded suit would be recommended to shorten the duration needed in real-time to adjust to the radiation dump.

  • $\begingroup$ potassium iodide works for radioactive fallout, preventing radioactive iodine from being incorporated into body. It does nothing for pure radiation. +1 anyway but please fix that part, because it's quite irritating mistake to find in books, at least for people who knows. $\endgroup$
    – Mołot
    Oct 23, 2018 at 9:37
  • $\begingroup$ Fixed. Doesn't look like there is anything currently known that would help the body better handle pure radiation exposure, but I admit my knowledge here is limited. If there is some way to prepare the body for high levels of radiation exposure over a short period of time, let me know and I'll update my answer to include it as an example. $\endgroup$
    – cpcodes
    Oct 23, 2018 at 16:37
  • $\begingroup$ Example of radiation treatment that looks possible: businesswire.com/news/home/20030407005484/en/… - No need to be that specific. Radiation treatments are possible, are there, in near-future settings can be used, why not. $\endgroup$
    – Mołot
    Oct 23, 2018 at 16:47
  • $\begingroup$ Okay, I'll just leave it as anti-rad treatment then. Thanks again. $\endgroup$
    – cpcodes
    Oct 23, 2018 at 17:05
  • $\begingroup$ "Time lapse view" as a feature ... awesome vacation! $\endgroup$
    – Harthag
    Oct 24, 2018 at 16:16

I'd go with "time slows down" interpretation. If radiation particle hits the capsule, it is slowed down at its boundary, and will be released once the field is turned off.

This obviously creates a problem as passenger will be bombarded by all the particles accumulated during their voyage.

I would recommend shielding the capsule from radiation and light during the voyage. Space stations are shielded anyway, and while capsule will require more shielding, there is also smaller area to shield. Or you can keep large number of capsules in a vault (less surface area than individual capsules).

Gravity change is inevitable, but effect is just a (near-)fall from standing position. Can't be that bad.

I hope you realize passenger cannot "exit" the capsule on their own accord. Somebody (or something) would have to shut down the field generator.

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    $\begingroup$ Might also be a good idea to use non- physical forms of shielding, such as electromagneticly repelling charged particles. That said, how gravity (and electromagnetism!) are affected by the boundary and interior volume would be weird. $\endgroup$ Oct 22, 2018 at 20:38

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